In the medieval history of Europe, Bulgaria's status as the Bulgarian Empire (Bulgarian: Българско царство, Balgarsko tsarstvo[ˈbəlɡɐrskʊ ˈt͡sarstvʊ]), wherein it acted as a key regional power (particularly rivaling Byzantium in Southeastern Europe[1]) occurred in two distinct periods: between the seventh and eleventh centuries, and again between the twelfth and fourteenth centuries. The two "Bulgarian Empires" are not treated as separate entities, but rather as one state restored after a period of Byzantine rule over its territory. Bulgaria is one of the few historic states and nations whose economy and society were never based on slavery, and slavery never played an important role in Bulgarian statehood development and wealth.

^Dvornik, Francis (1956). The Slavs: Their Early History and Civilization. Boston: American Academy of Arts and Sciences. p. 179. The Psalter and the Book of Prophets were adapted or "modernized" with special regard to their use in Bulgarian churches, and it was in this school that glagolitic writing was replaced by the so-called Cyrillic writing, which was more akin to the Greek uncial, simplified matters considerably and is still used by the Orthodox Slavs.